Collaborative Research: Experimental investigation of magmatic processes at Volcan Quizapu

Lead PI: Philipp Ruprecht

Unit Affiliation: Geochemistry, Lamont-Doherty Earth Observatory (LDEO)

March 2014 - February 2017
South America ; Chile
Project Type: Research

DESCRIPTION: Volcanic eruptions taking place along subduction zones (arcs) are commonly interpreted as triggered by the influx of new magma to their shallow storage systems. This project aims to explore the late-stage changes in temperature, pressure, water content, and composition of arc magmas on the "crystal cargo" they carry, by testing the premise that the textures and compositions of erupted materials preserve this chronology. Comparison of experimental and natural samples will shed light on magma chamber and transit processes occurring between magma mixing and eruption. Two historical eruptions of Volcan Quizapu (Chilean Andes), one effusive and one explosive, have been characterized petrologically and geochemically in prior studies. Evidence points to a magmatic system of predominantly dacite with single-episode, eruption-triggering influxes of andesitic magma. The relative simplicity of these interactions makes Quizapu an ideal starting point for a targeted experimental study addressing questions related to magma mixing and ascent/eruption. Key lines of inquiry include constraining resorption/de-stabilization kinetics of plagioclase and amphibole in response to perturbation, as these minerals preserve evidence of magma storage conditions prior to eruption. The goals of this investigation are to (1) establish pre-eruption environmental conditions of Quizapu dacite and andesite, (2) examine response times of key thermobarometers and hygrometers through a series of step-heating experiments, (3) explore the formation conditions of sieve-textured plagioclase, and (4) broadly examine crystal-scale responses to thermodynamic perturbations through high-resolution chemical analysis and diffusion modeling. The results will have general implications for magma mixing processes among intermediate-composition arc magmas, not only because the recharge-triggered Quizapu events are typical of arc volcanoes, but also because the crystal-scale processes on which the study focuses (the influence of halogens on amphibole composition and stability, plagioclase dissolution kinetics upon heating, and formation of sieve-texture via several proposed mechanisms) are germane to a broad spectrum of magmatic settings.